The magazine of the Melbourne PC User Group Camera to PC Interfaces Rick Gordon

Transferring the images from digital camera to a computer requires several more pieces of technology, most of which are standardised today. The first thing you need to determine is how the physical connection will be made. Secondly you need to determine the camera/computer software compatibility.
 
Hardware Choices

There are really only a few physical interface choices to worry about with a digital camera: you can connect it with an appropriate cable and/or you can use a flash card reader. This section will detail the options and their tradeoffs.

Flash Card (and MicroDrive)

Memory cards for digital cameras are often marketed under the term "digital film". Just as there are different sizes and types of film, there are different formats and sizes of memory cards, generically referred to as "flash cards".

There are several types of flash memory cards currently in use today, the most common being CompactFlash, SmartMedia, MultiMedia Card and Secure Digital, as well as proprietary formats such as Sony Memory Stick. Because cameras store images on the flash card using a standard format (DCF, described later in this article), this is a simple and efficient method of transferring images.

Besides the memory card for the camera, a card reader is also necessary to read the images from the card without connecting the camera. There are card readers available for all formats (and some that support multiple formats) that connect via USB or FireWire connections, and there are also adapters that allow their use in CardBus slots. CompactFlash cards actually come in two sizes: the thinner Type 1 size has been around the longest, and all of the solid-state cards currently available conform to it. The thicker Type 2 size is newer and is not accepted by all cameras.

The only media that comes in this format is MicroDrive - tiny hard drive mechanisms that currently store up to 1 GB. They are more shock sensitive than solid-state devices, and this must be taken into account during use. Currently they give the greatest amount of storage for the money, so they're something to consider.

SmartMedia memory, although smaller than CompactFlash, has also provided less capacity and has been more expensive than CompactFlash memory. Another issue with it, at least in the past, has been that cameras have required firmware upgrades to handle newer, larger capacity cards.

Secure Digital (SD) memory is less common in cameras - it too tends to be more expensive than CompactFlash, and contains a "secure" area that doesn't seem to be used by current cameras. Multi Media Card (MMC) is a similar card without this feature. Their other distinguishing feature is the size - half the size of CompactFlash cards (which aren't very big themselves!)

Sony MemoryStick is mainly used only in Sony devices, although a couple of other manufacturers have licensed it.

Flash card memory varies in speed, something that requires research before purchase. One common and misleading speed rating is used on CompactFlash media in particular. The speed rating there refers to the transfer speed relative to a CD-ROM device. A basic 1x CD-ROM device transfers at 150 KBps, not very fast in modern devices, so a higher rating (8x or 16x) is something to look for. Actual transfer speed will likely vary with your camera.

Digital cameras store their information on flash cards in DCF (Design rule for Camera File system), another standard from JEIDA, the Japanese manufacturers association. When the card is mounted, it will appear as a disk drive with the DCIM directory at its root.

i.Link/FireWire

Serial

There are still usable cameras around that connect via standard RS-232C serial interface. USB has for the most part replaced this interface in new products. The main problem with it is that it's 
going to be slow - speed would be measured in Kbps instead of Mbps.

Optical Disc

A few cameras out there have a CD or Mini-Disc recorder built in. These are not very common, but might work well for some people.

Wireless

A wireless connection is probably in the future for digital cameras, most likely something like Bluetooth. It would provide a fast and convenient connection method if and when it's actually implemented by the camera manufacturers.

Camera Software

When it comes down to it, a digital camera is just another specialized computer. As such, it has its own internal operating system, and it presents some form of interface to the other computers that want to communicate with it. We'll discuss the typical options available here. Note that many cameras may offer more than one interface, depending upon the host OS and the drivers installed thereon.

USB Mass Storage

PTP

Picture Transfer Protocol provides a more sophisticated view of the camera's pictures and other properties. Cameras that support PTP allow supporting software to retrieve Metadata from the pictures, the pictures themselves, and about the camera settings. Some cameras even allow the computer to control them through this interface, so that one can change their settings and even tell the camera to capture another image. On Windows XP and ME, such cameras should work with any applications that support its built-in WIA interface (described below) without additional drivers.

Proprietary

Although becoming less common, some cameras implement proprietary interfaces that only their software (or their licensed developers) can communicate with. These usually require the installation of a special driver, or an entire application, in order to access the camera features. Look for support of WIA 
or other standards described below.
 
Fortunately, documentation for these interfaces is often available to 3rd party developers, so there are other applications that support them as well.

Application Software Interface

Besides the camera software interface, there are also options on the application software side that affect its usage. The main question here is how applications on the computer communicate with the camera - either through built-in system software or through third-party standards. These are described in this section.

Windows Image Architecture

TWAIN

TWAIN (Technology Without An Interesting Name) is a common, complex interface used mainly for scanners rather than cameras. WIA provides rudimentary support for TWAIN-only devices, but generally the manufacturer provides a richer set of controls that can be accessed by a TWAIN-compliant application.

PS Plug-in

Devices that do not provide WIA or TWAIN support will often provide a PhotoShop Plug-In that allows applications to communicate with it. Generally this is used more by scanner than cameras. However, some camera manufacturers provide a plug-in to convert their RAW images into a standard raster image format.

Proprietary

Last but not least, there are cameras that support proprietary interfaces, and that thus require a vendor's application software to access and manipulate the camera and its images. While certainly less desirable in its flexibility, this still may be a workable solution for some.

Summary

The media chosen to capture images and the method used to transfer them to your computer is an important consideration when evaluating digital cameras. The choices made will affect your overall digital workflow and can be a source of aggravation if they don't meet your requirements.

In my opinion, flash cards, and their accompanying readers, provide the greatest flexibility: they're easily carried, readily available, and eliminate the need to hook up a cable when its time to upload the images. They provide a film-like experience with the advantage that you can reuse them.

About the Author
Rick Gordon, rgordon@oz.net is a software developer based in Seattle, WA. Recent projects included developing the camera interfaces in the Adobe PhotoShop Album product, and image and colour management support in the Adobe SVG Viewer plug-in. Rick is an avid amateur photographer who shoots a lot less film these days, but still likes black and white traditional processes.

Reprinted from the March 2003 issue of PC Update, the magazine of Melbourne PC User Group, Australia

[ About Melbourne PC User Group ]